The present invention relates to a battery saving circuit for use in a radio paging receiver or the like.
Battery saving circuits are generally employed for paging receivers in order to minimize power consumption. Such battery saving circuits function to selectively supply power to a receiver only during the time when selective calling signals of a group to which the receiver belongs are being transmitted and to cut the power supply during the time calling signals of other groups are being transmitted. One example of receivers including such a battery saving circuit is disclosed in U.S. Pat. No. 4,181,893 issued to E. L. Ehmke, Jan. 1, 1980.
A personal paging receiver includes a waveform-shaping circuit to provide rectangular waveform signals from received signals. The waveform-shaping circuit, in turn, includes a low-pass filter in order to obtain a reference voltage, and such a filter has a comparatively large time constant to stabilize the reference voltage. As a result, it takes a time equivalent to the time constant of the filter before the waveform-shaping circuit reaches normal operation. In the paging receiver, therefore, a battery saver circuit is started a time period, at least equal to the filter time constant, before the arrival of the selective calling signal of its own group. Such a battery saving circuit set at an earlier timing, however, is not desirable because, although it is effective for the waveform-shaping circuit, it consumes excessive power in other components of the pager receiver, thereby lowering the battery saving efficiency.